1. Field of the Invention
The invention relates to a method of laminating a plurality of sheets to a metallic substrate. More particularly, the invention relates to a method of laminating graphite sheets to a metallic substrate by use of a low melt metal coating applied to the metallic substrate as the means or adhesive for bonding the graphite sheets to the substrate to form a composite laminate.
2. Description of the Prior Art
Numerous types of inventions and procedures have been devised for securing together sheets of various materials to form a composite laminate. Most of these methods involve the applying of an organic adhesive to the substrate which serves as the bonding agent between the laminations. Various heating, cooling and pressure procedures and equipment for carrying out the such methods have been used, many of which are quite elaborate and expensive.
The use of organic adhesive type materials have proved satisfactory for most applications. However, difficulties have arisen when the laminated structure is used in an application in which it is subjected to high temperatures and various chemical solutions which destroy the adhesive bond between the substrate and attached sheets.
For example, problems have been encountered in the formation of laminated products, such as gaskets, for use in internal combustion engines which must withstand prolonged temperatures up to 400.degree.F and are subjected to Ethylene Glycol solutions for sustained periods of time from the engine coolant system. The use of known organic adhesives have proved unsatisfactory for such applications because of the sustained high temperatures, and/or harmful and destructive reactions with the Ethylene Glycol solution.
Likewise, many installations such as in internal combustion engines, furnaces, hot metal working procedures, refractories, heat exchanges, solar energy collecting panels, etc. have the need of laminated structures permitting the rapid transfer or conduction of heat therethrough. The use of organic adhesives, even if able to withstand the high temperatures encountered, act as an insulation to the transfer of heat through the laminate and prove unsatisfactory.
Also, laminated structures used for many applications have an asbestos or heat resistant material as the outer layers, which in turn is bonded to a metallic substrate. Such heat resistant material makes it extremely difficult to form multilayered laminated structure when the application of heat is required for the setting or bonding of the adhesive, since the heat is unable to penetrate satisfactorily through the heat resistant material to the innermost layer. This has necessitated the use of an organic adhesive not requiring heat for bonding, which proves unsuccessful for some applications.
Thus, a need exists for a method of forming laminated structures having a metallic substrate for strength, and heat conductive outer sheets, which sheets are bonded to the metallic substrate by use of a non-organic adhesive able to withstand high temperatures and many corrosive solutions.
It has been found that the use of graphite sheets when bonded to a metal substrate which have been coated with a lower melt metal, by using a portion of the substrate metal coating as the bonding agent or adhesive, provides a laminated structure suitable for such applications. Such a lamination provides a construction able to withstand high temperatures for long periods of time and rapidly conducts heat through the lamination, and is unaffected by many chemical solutions.
A known method of making a laminated structure having a metallic substrate which uses metal as the bonding agent instead of the above described and heretofore used organic adhesives, is shown in U.S. Pat. No. 2,188,721. The method described in this patent appears to provide a satisfactory solution in providing the type of laminated structures of the specified materials.
Methods such as shown in U.S. Pat. No. 2,188,721 use asbestos sheets or other types of heat insulating materials which are fed continuously from a roll of such material. These methods require spray chambers and hot dip metal coating facilities, all of which are expensive and require considerable space and facilities, in order to carry out the steps of such procedures.
U.S. Pat. No. 2,073,334 discloses another method whereby webs of asbestos are applied to a running strip of metal substrate, in which an interposed layer of metal functions as the adhesive. Again the described method requires that a hot strip coating facility be located adjacent the laminating facility so that the asbestos strip is applied to the substrate while the metal coating on the substrate is still in a molten or liquified state, immediately after passage of the substrate through the metal bath and prior to solidification on the substrate. Thus, again considerable expense, equipment, space and procedures are required to carry out the steps of such a laminating method.
There has long been a need existing in the art for some means of eliminating the expense and complicated procedures for forming laminated structures using metal as the adhesive, in order to overcome the problems encountered with organic type adhesives and insulation sheets.